Implantable medical device including eddy current reducing battery

ABSTRACT

An implantable device, such as a pacer, defibrillator, or other cardiac rhythm management device, can include one or more MRI Safe components. In an example, the implantable device includes a battery including a first electrode and a second electrode separate from the first electrode. The second electrode includes a first surface and a second surface. The second electrode includes a slot through the second electrode from the first surface toward the second surface. The slot extends from a perimeter of the second electrode to an interior of the second electrode. The slot is configured to at least partially segment a surface area of the second electrode to reduce a radial current loop size in the second electrode.

CLAIM OR PRIORITY

This application is a continuation of U.S. application Ser. No.14/445,864, filed Jul. 29, 2014, which is a continuation of U.S.application Ser. No. 12/980,993, filed Dec. 29, 2010, now issued as U.S.Pat. No. 8,841,019, which claims the benefit of U.S. ProvisionalApplication No. 61/291,585, filed on Dec. 31, 2009, under 35 U.S.C. §119(e), each of which is incorporated herein by reference in itsentirety.

BACKGROUND

Implantable medical devices (IMDs) can perform a variety of diagnosticor therapeutic functions. For example, an IMD can include one or morecardiac function management features, such as to monitor the heart or toprovide electrical stimulation to a heart or to the nervous system, suchas to diagnose or treat a subject, such as one or more electrical ormechanical abnormalities of the heart. Examples of IMDs can includepacers, automatic implantable cardioverter-defibrillators (ICDs), orcardiac resynchronization therapy (CRT) devices, among others. Nuclearmagnetic resonance imaging (MRI), is a medical imaging technique thatcan be used to visualize internal structure of the body. MRI is anincreasingly common diagnostic tool, but can pose risks to a person withan IMD, such as a patient undergoing an MRI scan or a person nearby MRIequipment, or to people having a conductive implant.

In a MR field, an item, such as an IMD, can be referred to as “MR Safe”if the item poses no known hazard in all MRI environments. In anexample, MR Safe items can include non-conducting, non-metallic,non-magnetic materials, such as glass, porcelain, a non-conductivepolymer, etc. An item can be referred to as “MR Conditional” in the MRfield if the item has been demonstrated to pose no known hazards in aspecified MRI environment with specified conditions of use (e.g., staticmagnetic field strength, spatial gradient, time-varying magnetic fields,RF fields, etc.). In certain examples, MR Conditional items can belabeled with testing results sufficient to characterize item behavior ina specified MRI environment. Testing can include, among other things,magnetically induced displacement or torque, heating, induced current orvoltage, or one or more other factors. An item known to pose hazards inall MRI environments, such as a ferromagnetic scissors, can be referredto as “MR Unsafe.”

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 illustrates a cut-away view of an IMD showing basic components ofthe IMD.

FIG. 2 illustrates a cut-away view of a battery including anun-segmented electrode.

FIG. 3A illustrates a cut-away view of an example of a battery includinga segmented electrode.

FIG. 3B illustrates a side view of two example electrodes of the batteryof FIG. 3A.

FIG. 3C illustrates a side view of two example electrodes of the batteryof FIG. 3A.

FIGS. 4-10 illustrate examples of segmented electrodes.

FIG. 11 illustrates a perspective view of an example of a segmentedelectrode.

FIG. 12 illustrates a side view of the segmented electrode of FIG. 11.

FIG. 13 illustrates a perspective view of the segmented electrode ofFIG. 11 including insulating material within slots of the segmentedelectrode.

FIG. 14 illustrates a cut-away view of an example of a battery includinga segmented electrode including insulating material.

FIG. 15 illustrates a side view of the segmented electrode of FIG. 14.

FIG. 16 illustrates a side view of an example of an electrode prior topressing layers of the electrode together.

FIG. 17 illustrates a side view of the electrode of FIG. 16 afterpressing together of the layers of the electrode.

FIG. 18 illustrates a side view of an example of an electrode prior topressing layers of the electrode together.

FIG. 19 illustrates a side view of the electrode of FIG. 18 afterpressing together of the layers of the electrode.

FIG. 20 illustrates a side view of an example of an electrode prior topressing layers of the electrode together.

FIG. 21 illustrates a side view of the electrode of FIG. 20 afterpressing together of the layers of the electrode.

DETAILED DESCRIPTION

Nuclear magnetic resonance (NMR) devices (e.g., an MRI scanner, an NMRspectrometer, or other NMR device) can produce both static andtime-varying magnetic fields. For example, an MRI scanner can provide astrong static magnetic field, B₀, such as to align nuclei within asubject to the axis of the B₀ field. The B₀ can provide a slight netmagnetization (e.g., a “spin polarization”) among the nuclei in bulkbecause the spin states of the nuclei are not randomly distributed amongthe possible spin states. Because the resolution attainable by NMRdevices can be related to the magnitude of the B₀ field, a stronger B₀field can be used to spin polarize the subject's nuclei to obtain finerresolution images. NMR devices can be classified according the magnitudeof the B₀ field used during imaging, such as a 1.5 Tesla B₀ field, a 3.0Tesla B₀ field, etc.

After nuclei are aligned using the B₀ field, one or more radio frequency(RF) magnetic excitation pulses can be delivered such as to alter thealignment of specified nuclei (e.g., within a particular volume or planeto be imaged within the subject). The power, phase, and range offrequencies of the one or more RF excitation pulses can be selected,such as depending on the magnitude of the B₀ field, the type or resonantfrequency of the nuclei to be imaged, or one or more other factors.After the RF excitation pulses are turned off, one or more RF receiverscan be used to detect a time-varying magnetic field (e.g., a flux)developed by the nuclei as they relax back to a lower energy state, suchas the spin polarized state induced by the static magnetic field, B₀.

One or more gradient magnetic fields can also be provided during MR,such as to create a slight position-dependent variation in the staticpolarization field. The variation in the static polarization fieldslightly alters the resonant frequency of the relaxing nuclei, such asduring relaxation after excitation by the one or more RF pulses. Usingthe gradient field along with the static field can provide “spatiallocalization” of signals detected by the RF receiver, such as by usingfrequency discrimination. Using a gradient field allows a volume orplane to be imaged more efficiently. In a gradient field example,signals received from relaxing nuclei can include energy in respectiveunique frequency ranges corresponding to the respective locations of thenuclei.

Active MRI equipment can induce unwanted torques, forces, or heating inan IMD or other conductive implant, or can interfere with operation ofthe IMD. In certain examples, the interference can include disruption insensing by the IMD, interference in communication between the IMD andother implants or external modules during MRI operation, or disruptionin monitoring or therapeutic function of the IMD.

During an MRI scan, the one or more RF excitation pulses can includeenergy delivered at frequencies from less than 10 MHz to more than 100MHz, such as corresponding to the nuclear magnetic resonances of thesubject nuclei to be imaged. The gradient magnetic field can includeenergy delivered at frequencies lower than the RF excitation pulses,because most of the AC energy included in the gradient field is providedwhen the gradient field is ramping or “slewing.” The one or moregradient magnetic fields can be provided in multiple axes, such asincluding individual time-varying gradient fields provided in each ofthe axes to provide imaging in multiple dimensions.

In an example, the static field, B₀, can induce unwanted forces ortorques on ferromagnetic materials, such as steel or nickel. The forcesor torques can occur even when the materials are not directly within the“bore” of the MRI equipment—because significant fields can exist nearthe MRI equipment. Moreover, if an electric current is switched on oroff in the presence of the B₀ field, a significant torque or force canbe suddenly imposed in the plane of the circulation of the current, eventhough the B₀ field itself is static. The induced force or torque can beminimal for small currents, but the torque can be significant for largercurrents, such as those delivered during defibrillation shock therapy.For example, assuming the circulating current is circulating in a planenormal (e.g., perpendicular) to the static field, the torque can beproportional to the magnitude of the B₀ field, multiplied by the surfacearea of the current loop, multiplied by the current.

Time-varying fields, such as the gradient field or the field associatedwith the RF excitation pulse, can present different risks than thestatic field, B₀. For example, the behavior of a wire loop in thepresence of a time-varying magnetic field can be described usingFaraday's law, which can be represented by

${ɛ = {- \frac{d\;\Phi_{B_{1}}}{dt}}},$in which ε can represent the electromotive force (e.g., in volts), suchas developed by a time-varying magnetic flux. The magnetic flux can berepresented as

$\Phi_{B\; 1} = {\underset{S}{\int\int}{B_{1} \cdot {{dS}.}}}$in which B₁ can represent an instantaneous magnetic flux density vector(e.g., in Webers per square meter, or Tesla). If B₁ is relativelyuniform over the surface S, then the magnetic flux can be approximatelyΦ_(B1)=|B₁∥A|, where A can represent the area of the surface S.Operating MRI equipment can produce a time-varying gradient field havinga slew rates in excess of 100 Tesla per second (T/s). The slew rate canbe similar to a “slope” of the gradient field, and is thus similar to

$\frac{d\;\Phi_{B_{1}}}{dt}.$

The electromotive force (EMF) of Faraday's law can cause an unwantedheating effect in a conductor—regardless of whether the conductor isferromagnetic. EMF can induce current flow in a conductor (e.g., ahousing of an IMD, one or more other conductive regions within an IMD,or one or more other conductive implants). The induced current candissipate energy and can oppose the direction of the change of theexternally applied field (e.g., given by Lenz's law). The inducedcurrent tends to curl away from its initial direction, forming an “eddycurrent” over the surface of the conductor, such as due to Lorentzforces acting upon electrons moving through the conductor. Becausenon-ideal conductors have a finite resistivity, the flow of inducedcurrent through the conductor can generate heat. The induced heat cancause a significant temperature rise in or near the conductor over theduration of the scan. The eddy current power deposition can beproportional to the square of both the peak flux density and thefrequency of the excitation. If significant heating occurs, it can causetissue damage or death.

As described above, the MRI time varying gradient fields can induce eddycurrents and heat within conductive components of the IMD. Additionally,these eddy currents can generate a magnetic moment producing a torque inthe direction that aligns the eddy current magnetic moment with the MRIB₀ field. This torque can produce differential forces (and, in turn,vibration) between the internal components of the IMD and/or itsenclosure. The resulting vibration of internal components can causecyclical fatigue failures, for example between the battery terminal andits electrical connection to electronic subassemblies, such as amicroelectronic hybrid circuit board, which can render the IMDinoperable and require premature surgical replacement. In light of this,the present inventors have recognized that induced heat and vibrationcan present hazards to the patient having an IMD and being subjected toan MRI environment.

Generally, induced currents, such as induced by the RF magneticexcitation pulse, can concentrate near the surface of a conductor, aphenomenon that can be referred to as the skin effect. The skin effectcan limit both the magnitude and depth of the induced current, thusreducing power dissipation. However, the gradient field can includeenergy at a much lower frequency than the RF magnetic excitation field,which can more easily penetrate through the housing of the IMD. Unlikethe field from the RF excitation pulse, the gradient field can moreeasily induce bulk eddy currents in one or more conductors within theIMD housing, such as within one or more circuits, capacitors, batteries,or other conductors.

Aside from heating, the MRI gradient induced EMF can create, among otherthings, non-physiologic voltages that can cause erroneous sensing ofcardiac electrical activity, or the EMF can create a voltage sufficientto depolarize cardiac tissue or render the cardiac tissue refractory,possibly affecting pacing therapy. In an illustrative example, an IMDcan be connected to one or more leads, such as one or more subcutaneousor intravascular leads positioned to monitor the patient, or to provideone or more therapies to the patient. In this illustrative example, asurface area of a “circuit” including the lead, the housing of the IMD,and a path through at least partially conductive body tissue between anelectrode on the lead and the IMD housing can be more than 300 squarecentimeters, or more than 0.03 square meters. Thus, using Faraday's law,the electromotive force (EMF) developed through the body tissue betweenthe electrode (e.g., a distal tip or ring electrode) of the lead and thehousing of the IMD can be more than 0.03 square meters times 100 t/s, ormore than 3 volts.

The present inventors have recognized, among other things, that it isdesirable for IMDs to include increased safety within an MRIenvironment. For instance, the present inventors have recognized that itis desirable for IMDs to include a decreased response to the magneticfields present within or otherwise proximate an MRI device. Suchresponses include, but are not limited to, heating, vibration or otherinduced movement, induced voltages, and the like. In some examples, thepresent inventors have recognized that it is desirable to reduce themagnetic field response of IMD batteries.

Referring to FIG. 1, an example of an IMD 100 is shown. The IMD 100, inan example, includes a header 102 for attaching a component such as alead to the IMD. In an example, the IMD 100 includes an electronicmodule 104 including electronics of the IMD 100 associated with theoperation and functioning of the IMD 100 within a patient. In someexamples, the IMD 100 includes a cell or battery 106. In variousexamples, one of more of the components 102, 104, 106, or othercomponents of IMDs which are not shown in FIG. 1, such as capacitors,leads, etc., can include decreased response to magnetic fields forincreased safety within the MRI environment. As such, the descriptionherein, although describing primarily decreased MR response inbatteries, can be applied to any components or combinations ofcomponents of an IMD, including also metal or otherwise conductiveenclosures of the components of the IMD or of the IMD itself. Examplesof IMDs that can include metal enclosures and/or internal large surfacearea components include but are not limited to, cardiac pacemakers;automatic implantable cardioverter-defibrillators (ICDs); cardiacresynchronization therapy and defibrillator (CRT-D) devices;neuromodulators including deep brain stimulators (DBS), various paincontrol devices, and lead systems for stimulation of the spinal cord,muscles, and other nerves of the body (such as, for instance, the vagalnerve); implantable diagnostic devices for monitoring cardiac function;cochlear implants; and drug pumps for administering periodic or demandbased pharmacological therapy. In general, it is contemplated that thepresent description can relate to or be applied to any IMDs that havemetallic enclosures and/or include relatively large surface areainternal conductive components, which can circulate eddy currents inresponse to the MRI time varying gradient magnetic fields to cause heatand/or vibration in the IMD.

Referring to FIG. 2, a battery 206 for an IMD includes a housing 208that is partially cut away to show an electrode 210 of the battery 206.An arrow 212 is depicted on the electrode 210 to portray an exampleradial current or eddy current of the electrode 210, such as could beinduced by a gradient field of an MRI device. In an example, an inducededdy current can interact with the static magnetic field and can resultin vibration or other movement of the battery 206. In another example,the induced eddy current can be dissipated as heat to elevate thetemperature of the battery 206. For a given time varying gradient field,the induced torque and/or generated heat are functions of the materialand the geometry of the electrode 210. For instance, the eddy currentinduced heating and vibration are generally proportional to the squareof the surface area of the conductor, or, in the example of FIG. 2,generally the area encompassed by the induced eddy current shown byarrow 212. Because of the relatively large surface area (and therelatively large loop 212 of the eddy current) of the example electrode210, the battery 206 can be a substantial source of heat and/orvibration when placed within an MRI environment. Accordingly, reductionof the loop size of an induced eddy current present in, for instance, anelectrode of a battery of an IMD, is contemplated herein to reduceheating and/or movement induced in an IMD subjected to an MRIenvironment. Several examples of such electrodes are described below.

Referring to FIG. 3A, in an example, a battery 306, for use, forinstance, in an IMD, includes a housing 308 that is shown partially cutaway to show a segmented electrode 310 of the battery 306. In someexamples, the segmented electrode 310 includes high resistance sectionsto segment the electrode 310. In some examples, the high resistancesections are formed by at least partially cutting through the electrode310. In further examples, the segmented electrode 310 includes one ormore openings or slots 314. In an example, the segmented electrode 310includes two openings or slots 314 extending from a perimeter of theelectrode 310 to an interior portion of the electrode 310. In furtherexamples, more or less than two slots can be formed in the electrode. Instill further examples, the one or more slots can be formed in differentareas of the electrode. In the example shown in FIG. 3A, the slots 314provide breaks in the surface area of the electrode 310, which canresult in smaller radial current loops of eddy currents (relative to theloop size of the eddy current of an unsegmented electrode, such as theexample electrode 210 of FIG. 2), as depicted by arrows 312A, 312B,312C. By reducing the loop size of the eddy currents in the electrode310, in an example, the heating and/or movement induced by an MRIenvironment can be reduced to a level at which the IMD and/or thebattery 306 of the IMD are deemed MRI Safe. Because removal of electrodematerial can generally adversely affect performance and effectiveness(longevity, for instance) of the battery 306, a consideration insegmentation of the electrode 310 is minimal material removal. In anexample, by optimizing a pattern of the segmentation of the electrode310, the performance of the battery 306 can be minimally impacted while,at the same time, sufficiently minimizing eddy current loop size toresult in an MRI Safe battery 306.

Referring now to FIGS. 3A and 3B, in an example, the battery 306includes a first electrode 320. A second electrode (such as, thesegmented electrode 310) is separate from the first electrode 320. In anexample, the second electrode 310 includes a first surface 310A facingthe first electrode 320 and an oppositely disposed second surface 310Bfacing away from the first electrode 320. In an example, the first andsecond electrodes are separated by a relatively small distance. In afurther example, the first and second electrodes 320, 310 are separatedby a battery separator, such as, for instance, a separator membrane. Inan example, the first and second electrodes 320, 310 includesubstantially similar footprints. The second electrode 310, in anexample, includes one or more slots 314, which extend through the secondelectrode 310 from the first surface 310A toward the second surface310B. In an example, the one or more slots 314 extend completely throughthe second electrode 310 from the first surface 310A to the secondsurface 310B. The one or more slots 314, in an example, extend from aperimeter of the second electrode 310 to an interior of the secondelectrode 310. The one or more slots 314 can be configured to at leastpartially segment a surface area of the second electrode 310 to reduce aradial current loop size (as depicted by arrows 312A, 312B, 312C) in thesecond electrode 310. In some examples, depending on the conductivity,thickness, and number of first electrodes 320, it can be desirable tosegment the first electrode 320 to reduce the overall heating of thebattery to level that results in a MR conditionally safe design. Inother examples, depending upon the constitutive materials and geometricform of the one or more first electrodes 320, it can be desirable tosegment in the one or more first electrodes 320.

In an example, the first electrode 320 includes a cathode and the secondelectrode 310 includes an anode. In further examples, although shown inFIG. 3B with one first electrode 320 and one second electrode 210, thebattery 306 can include more than one first electrode 320 and/or morethan one second electrode 310, depending upon the power requirements ofthe IMD or other device within which the battery 306 is to be used. Inan example, the first electrode 320 can be substantially planar. Inanother example, the second electrode 310 can be substantially planar.In other examples, the first and second electrodes 320, 310 can benon-planar.

Referring to FIG. 3B, in an example, the second electrode 310 includes afirst layer 316 forming the first surface 310A of the second electrode310 and a second layer 318 abutting the first layer 316, the secondlayer 318 forming the second surface 310B of the second electrode 310.In an example, the first layer 316 includes lithium. In some examples,the second layer 318 can include a conductive material. In an example,the second layer 318 can include nickel. In a further example, thesecond layer 318 includes stainless steel. In this example, due to themalleability of lithium, a relatively stiff second layer 318 isdesirable in order to maintain the lithium first layer 316 in thedesired shape. Moreover, a non-ferromagnetic material is also desirableto further decrease magnetic response to the MRI environment. For atleast these reasons, the stainless steel second layer 318 iscontemplated for use in the second electrode 310. However, it is furthercontemplated in other examples that other materials can be used for thesecond layer 318 provided that the materials provide a stiff backingmember for the lithium first layer 316 while, at the same time,providing a decreased response to magnetic fields present in the MRIenvironment.

In an example, the second layer 318 can be a mesh-like backing member toallow for increased engagement between the first and second layers 316,318. That is, in an example, when the lithium first layer 316 is pressedagainst the second layer 318, the malleable lithium deforms within voidsof the mesh-like second layer 318 to engage the first and second layers316, 318. In other examples, second layers 318 including other patternscan be used for engagement of the first and second layers 316, 318. Instill another example, the second layer 318 can be a flat sheet and anadhesive or other bonding compound can be used to engage the first andsecond layers 316, 318 of the second electrode.

In an example, the one or more slots 314 extend through at least thefirst layer. In an example in which the first layer 316 includeslithium, it is desirable for the one or more slots 314 to extend throughthe lithium first layer 316 to decrease magnetic response of the secondelectrode 310. Because of the high conductivity of lithium, the lithiumfirst layer 316 can be particularly susceptible to induced heat andmovement within an MRI environment.

For at least this reason, it is desirable to segment the lithium firstlayer 316 of the second electrode 310. In an example in which the secondlayer 318 includes stainless steel, the second layer 318 need not besegmented due to decreased response of stainless steel within the MRIenvironment. However, in another example, the one or more slots 314 canextend through the second layer 318 as well as the first layer 316. Inan example, both the first and second layers 316, 318 can be segmentedfor ease of manufacture of the second electrode 310. For instance, whendie pressing is used to segment the second electrode 310, both of thefirst and second layers 316, 318 can be segmented after the first andsecond layers 316, 318 are engaged. In another example, the second layer318 can remain un-segmented by segmenting the first layer 316 using diepressing prior to engagement of the first and second layers 316, 318 andthen engaging the segmented first layer 316 to the un-segmented secondlayer 318.

In various examples, the battery 306 can include a second electrodedifferently configured from the second electrode 310 described above.The configuration of the second electrode can depend on various factorsincluding performance requirements of the battery 306, type of devicebeing powered by the battery 306, or the like. Referring to FIG. 3C, inan example, the battery 306 can include a segmented second electrode310′ that is substantially similar to the second electrode 310 describedabove, but further includes a third layer 322 abutting the second layer318 along a surface of the second layer 318 facing away from the firstlayer 316, such that the second layer 318 is disposed between the firstand third layers 316, 322. In an example, the third layer 322 includes asimilar material to the material of the first layer 316. In a furtherexample, both the first and third layers 316, 322 include lithium. Inanother example, the third layer 322 can include a material differentthan the material of the first layer 316. In an example, the third layer322 can be segmented. For instance, in an example, the second electrode310′ can include one or more slots 324 extending through the third layer322. In one example, the slots 324 of the third layer 322 are alignedwith the one or more slots 314 of the first layer 316. In anotherexample, the slots 324 of the third layer 322 are offset from orotherwise out of alignment with the one or more slots 314 of the firstlayer 316.

Referring now to FIGS. 4-10, various examples of segmented secondelectrodes can include variously configured high resistance sections orsegmentations to break up surface areas of the second electrodes toreduce the size of radial current loops and reduce the response of thesecond electrodes within the MRI environment.

For instance, with respect to FIGS. 4-6, segmented second electrodes410, 510, 610 can include variously configured slots 414, 514, 614,although it is contemplated that other slot or opening configurationscan be used other than those shown herein, provided the slots oropenings provide segmentation and decreased response of the secondelectrodes within the MRI environment.

Referring to FIGS. 7-9, in further examples, segmented second electrodes710, 810, 910 can include thinning of the second electrodes 710, 810,910 along lines 714, 814, 914 to break up surface areas of the secondelectrodes 710, 810, 910. Such thinning of the second electrodes 710,810, 910 can be accomplished by, for instance, scoring, embossing, orcutting the second electrodes 710, 810, 910 along the lines 714, 814,914.

Referring to FIG. 10, in another example, a segmented electrode 1010includes one or more high resistance sections 1014. In various examples,the high resistance sections 1014 can be created in various ways. Insome examples, the one or more high resistance sections 1014 can becreated by oxidation or other chemical reactions. In some examples,masking can be used to control oxidation or other chemical reactionsused in creating the one or more high resistive sections 1014.

In an example, a positive photo resistive coating can be applied to theelectrode 1010. A mask can then be applied to the electrode 1010 and alight source, such as, for instance, an ultraviolet light source, can beapplied to decompose the photo resistive coating that is exposed throughthe mask. The electrode 1014 can then be subjected to an oxidationchamber, such as, for instance, an oxygen plasma chamber, to etch awaythe electrode that is not covered by photo resistive material. Dependingon the exposure time in the oxidation chamber, the exposed portion willbe oxidized, creating the one or more high resistance sections 1014 thatprovide a higher resistance pathway than the remainder of the segmentedelectrode 1010 and, in turn, provide segmentation and decreased responseof the segmented electrode 1010 within the MRI environment.

In another example, the segmented electrode 1010 includes insulation oranother relatively high resistance material embedded in the segmentedelectrode 1010 to form one or more high resistance sections 1014. Instill another example, the segmented electrode 1010 includes insulationor another relatively high resistance material constructed into thesegmented electrode 1010 to form one or more high resistance sections1014. In these examples, the one or more high resistance sections 1014provide segmentation and decreased response of the segmented electrode1010 within the MRI environment. That is, the one or more highresistance sections 1014 can break the path of induced eddy currents bythe gradient field of the MRI environment, thereby decreasing batteryheating and/or vibration.

Referring to FIGS. 11-15, in some examples, a second electrode 1110includes an insulating or separating material 1140 within one or morehigh resistance sections. In some examples, the one or more highresistance sections include one or more openings or slots 1114 in thesecond electrode 1110. The separating material 1140 can be includedwithin the one or more slots 1114, for instance, to inhibit dendriticgrowth across the one or more slots 1114 or to aid in manufacturing easewhile removing a relatively small or minimal amount of electrodematerial. Dendritic growth of the second electrode 1110 can result inrenewed connection of portions of the second electrode 1110 across theone or more slots 1114, which can result in larger radial current loopsin the second electrode 1114 and reduce the effectiveness of thesegmentation of the second electrode 1114. That is, dendritic growthacross the one or more slots 1114 can allow a conductive connection ofthe portions of the second electrode 1110 previously separated by theone or more slots 1114 to allow relatively large radial current loops inthe second electrode 1110, resulting in increased response of the secondelectrode 1110 to an MRI environment. Depending on the amount ofdendritic growth, segmentation of the second electrode 1110 can becomeineffective and result in an MRI Unsafe electrode. In an example, byinserting an insulative material in slots 1114, separated surface areascan be created to reduce current loop radius while still maintaining arelatively high amount of material in the electrode. In variousexamples, the separating material 1140 can be configured to maintainseparation of the second electrode 1114 along a length of the one ormore slots 1114 and inhibit the possibility of dendritic growth acrossthe one or more slots 1114 of the second electrode 1110.

In an example, a first layer 1116 of the second electrode 1110 can besheared to create a tab 1115 raised from a plane of the first layer1116, as seen in FIGS. 11 and 12. Shearing of the first layer 1116 canbe accomplished, in an example, using a die pressing operation. Shearingof the first layer 1116 can create the slots 1114 in the first layer1116 of the second electrode 1110. Once the tab 1115 is raised, theseparating material 1140 can be positioned between the raised tab 1115and the remainder of the second electrode 1110, as seen in FIG. 13. Withthe separating material 1140 in place, the raised tab 1115 can then bepressed back down in plane with the remainder of the first layer 1116 tocapture portions of the insulating material 1140 within the slots 1114to provide separation of the first layer 1116 along a length of each ofthe slots 1114, as shown in FIGS. 14 and 15. In various examples, abacking member or other second layer, such as those described above, canthen be engaged with the first layer 1116. In another example, the tab1115 can be flattened and the first layer can be engaged with the secondlayer in the same pressing operation. By segmenting the second electrode1110 in this way, little or no material of the first layer 1116 is lost,which can limit any reductions in effectiveness or performance of thesecond electrode 1110 resulting from segmentation of the secondelectrode 1110. In some examples, portions 1140A of the separatingmaterial 1140 overlapping the first layer 1116 can mask the first layer1116, which can result in decreased performance or effectiveness of thesecond electrode 1110. In an example, by keeping the amount of overlapof the portions 1140A to a minimum, reductions in performance oreffectiveness of the second electrode 1110 can be kept to a minimum.

Referring to FIGS. 16 and 17, in another example, a second electrode1610 includes one or more high resistance sections including aninsulating or separating material 1640 within one or more openings orslots 1614 in the second electrode 1610 to inhibit material growthacross the one or more slots 1614. In this example, the second electrode1610 includes a backing member or second layer 1618 abutting a firstlayer 1616. In an example, the second layer 1618 includes one or moretabs 1619 extending from a surface of the second layer 1618. In anexample, the second layer 1618 and/or the one or more tabs 1619 of thesecond layer 1618 provide the insulating or separating material 1640 ofthe second electrode 1610. In a further example, the first layer 1616includes lithium. In some examples, the second layer 1618 can include aconductive material. In a further example, the second layer 1618 caninclude stainless steel. In a still further example, the second layer1618 can include nickel. In another example, the first layer 1616 can bepositioned in correspondence with the second layer 1618 in asubstantially stacked manner, as shown in FIG. 16. In another example,the second layer 1618 can include nickel. The first and second layers1616, 1618 can then be pressed together in the direction of the arrowsshown in FIG. 16. During the pressing operation, the one or more tabs1619 can be pushed through the first layer 1610, thereby forming one ormore slots 1614 (the number and location of the one or more slots 1614corresponding to the number and location of the one or more tabs 1619 ofthe second layer 1618) in the first layer 1616 and, at the same time,filling the one or more slots 1614 with the separating material 1640, asshown in FIG. 17, to inhibit material growth across the one or moreslots 1614. In an example, the second layer 1618 and the one or moretabs 1619 of the second layer 1618 can be formed from the same material,such as, for instance, stainless steel. In another example, the one ormore tabs 1619 can be formed from a material different than the materialof the remainder of the second layer 1618, and the one or more tabs 1619can be engaged to the surface of the second layer 1618 in the desiredposition.

Referring to FIGS. 18 and 19, in further examples, a second electrode1810 includes one or more high resistance sections including aninsulating or separating material 1840 within one or more openings orslots 1814 in the second electrode 1810 to inhibit material growthacross the one or more slots 1814. In this example, the second electrode1810 includes a backing member or second layer 1818 abutting a firstlayer 1816. In an example, the second layer 1818 includes one or morevoids 1819 in the second layer 1818. In a further example, the secondelectrode 1810 can include a separation layer 1850 including theinsulating or separating material 1840 of the second electrode 1810. Theseparation layer 1850 can include one or more tabs 1852 extending from asurface of the separation layer 1850. In a further example, the firstlayer 1816 includes lithium. In some examples, the second layer 1818 caninclude a conductive material. In a further example, the second layer1818 can include stainless steel. In a still further example, the secondlayer 1818 can include nickel. In this example, the separation layer1850 need not be formed from the same material as the second layer 1818(for instance, stainless steel) and can be formed from any material withsufficient properties to allow pressing of the one or more tabs 1852through the first layer 1816, as described below, and to providesufficient separation of the segmented first layer 1816. In an example,the first layer 1816, the second layer 1818, and the separation layer1850 can be positioned in a substantially stacked manner, as shown inFIG. 18. In an example, the one or more tabs 1852 of the separationlayer 1850 are aligned with a corresponding number of voids 1819 of thesecond layer 1818. The first layer 1816, the second layer 1818, and theseparation layer 1850 can then be pressed together in the direction ofthe arrows shown in FIG. 18. During the pressing operation, the one ormore tabs 1852 of the separation can be directed through the one or morevoids 1819 of the second layer 1818 and can be pushed through the firstlayer 1816, thereby forming one or more slots 1814 (the number andlocation of the one or more slots 1814 corresponding to the number andlocation of the one or more tabs 1852 of the separation layer 1850) inthe first layer 1816 and, at the same time, filling the one or moreslots 1814 with the separating material 1840, as shown in FIG. 19, toinhibit material growth across the one or more slots 1814. In anexample, the separation layer 1850 and the one or more tabs 1852 of theseparation layer 1850 can be formed from the same material, such as, forinstance, a polymeric material. In other examples, the separation layer1850 and the one or more tabs 1852 are formed from a plastic material.In another example, the one or more tabs 1852 can be formed from amaterial different than the material of the remainder of the separationlayer 1850, and the one or more tabs 1852 can be engaged to the surfaceof the separation layer 1850 in the desired position.

Referring to FIGS. 20 and 21, in another example, a second electrode2010 includes one or more high resistance sections including aninsulating or separating material 2040 within one or more openings orslots 2014 in a first layer 2016 of the second electrode 2010 and withinone or more openings or slots 2024 in a third layer 2022 of the secondelectrode 2010 to inhibit material growth across the one or more slots2014 of the first layer 2016 and the one or more slots 2024 of the thirdlayer 2022. In this example, the second electrode 2010 includes abacking member or second layer 2018 abutting and sandwiched between thefirst layer 2016 and the third layer 2022. In an example, the secondlayer 2018 includes one or more tabs 2019 extending from a first surfaceof the second layer 2018 and one or more tabs 2019 extending from asecond surface of the second layer 2018. In an example, the second layer2018 and/or the one or more tabs 2019 of the second layer 2018 providethe insulating or separating material 2040 of the second electrode 2010.In a further example, the first and third layers 2016, 2022 includeslithium. In some examples, the second layer 2018 can include aconductive material. In a further example, the second layer 2018 caninclude stainless steel. In a still further example, the second layer2018 can include nickel. In a further example, the first, second, andthird layers 2016, 2018, 2022 can be positioned in a substantiallystacked manner, as shown in FIG. 20. The first, second, and third layers2016, 2018, 2022 can then be pressed together in the direction of thearrows shown in FIG. 20. During the pressing operation, the one or moretabs 2019 of the first surface of the second layer 2018 can be pushedthrough the first layer 2010 and the one or more tabs 2019 of the secondsurface of the second layer 2018 can be pushed through the third layer2022, thereby forming one or more slots 2014 (the number and location ofthe one or more slots 2014 corresponding to the number and location ofthe one or more tabs 2019 of the first surface of the second layer 2018)in the first layer 2016 and forming one or more slots 2024 (the numberand location of the one or more slots 2024 corresponding to the numberand location of the one or more tabs 2019 of the second surface of thesecond layer 2018) in the third layer 2022. At the same time, thispressing operation can fill the one or more slots 2014 of the firstlayer 2016 and the one or more slots 2024 of the third layer 2022 withthe separating material 2040, as shown in FIG. 21, to inhibit materialgrowth across the one or more slots 2014, 2024. In an example, the oneor more tabs 2019 of the first surface of the second layer 2018 aresubstantially aligned with the one or more tabs 2019 of the secondsurface of the second layer 2018. In another example, the one or moretabs 2019 of the first surface of the second layer 2018 are offset fromor otherwise not aligned with the one or more tabs 2019 of the secondsurface of the second layer 2018. In further examples, the number oftabs 2019 of the first surface of the second layer 2018 can be greaterthan or less than the number of tabs 2019 of the second surface of thesecond layer 2018. In an example, the second layer 2018 and the one ormore tabs 2019 of each of the first and second surfaces of the secondlayer 2018 can be formed from the same material, such as, for instance,stainless steel. In another example, the one or more tabs 2019 of eachof the first and second surfaces of the second layer 2018 can be formedfrom a material different than the material of the remainder of thesecond layer 2018, and the one or more tabs 2019 can be engaged to eachof the first and second surfaces of the second layer 2018 in the desiredposition. In another example, it is contemplated that backing materialswith voids corresponding to the tabs 2019 of the second layer 2018 canbe used in a manner similar to that described above with respect toFIGS. 18 and 19.

The above described examples illustrate segmented components of an IMDand methods of making such segmented IMD components, with such segmentedcomponents including a reduced response (as compared to un-segmentedcomponents) to magnetic fields present in an MRI environment. In someexamples, such segmentation can be included in IMD batteries. In furtherexamples, electrodes, including anodes and/or cathodes, of IMD batteriescan be segmented in order to make the IMD battery MRI Safe. Bysegmenting IMD components as described above, the present inventors haverecognized that eddy currents in the IMD components can be reduced,thereby resulting in reduced heating and/or vibration of the segmentedcomponents when exposed to an MRI environment. In this way, examples ofthe segmented IMD components and methods, such as those described above,can be used in various IMDs to make such IMDs MRI Safe.

Additional Notes

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

All publications, patents, and patent documents referred to in thisdocument are incorporated by reference herein in their entirety, asthough individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document, forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The claimed invention is:
 1. An implantable medical device batterycomprising: a first electrode; and a second electrode separate from thefirst electrode, the second electrode including: a first layer formed ofa first material having a first continuous surface and a secondcontinuous surface opposite the first continuous surface, the firstmaterial being a conductive material; and a second layer positioned onthe first continuous surface of the first layer, the second layer formedof a second material different from the first material, wherein thesecond material is lithium, wherein the second layer includes a firstportion separated from a second portion by a first high resistancesection, the first high resistance section having a greater resistancecompared to the first and second portions of the second layer to reducea radial current loop size in the second electrode.
 2. The implantablemedical device of claim 1, wherein the first surface and the secondsurface of the first layer are continuous surfaces.
 3. The implantablemedical device of claim 1, wherein the first high resistance section,along a cross-sectional view, is defined by a first surface of the firstportion, a third portion of the first surface of the first layer, and asecond surface of the second portion.
 4. The implantable medical deviceof claim 1, wherein the conductive material is selected from one ofstainless steel and nickel.
 5. The implantable medical device of claim1, wherein the first high resistance section is formed by a first gapbetween the first and second portions of the second layer.
 6. Theimplantable medical device of claim 5, wherein the first layer includesat least one tab extending from the first surface of the first layer,wherein the tab is positioned within the first gap between the first andsecond portions of the second layer.
 7. The implantable medical deviceof claim 6, wherein the tab is formed of the first material.
 8. Theimplantable medical device of claim 6, wherein the tab is formed of athird material different from the first material.
 9. The implantablemedical device of claim 6, wherein the first layer includes at least onetab extending from the second surface of the first layer.
 10. Theimplantable medical device of claim 9, wherein the second electrodefurther includes: a third layer positioned on the second surface of thefirst layer, the third layer formed of the second material, wherein thethird layer includes a third portion separated from a fourth portion bya second high resistance section, the second high resistance sectionhaving a greater resistance compared to the third and fourth portions ofthe third layer to reduce a radial current loop size in the secondelectrode.
 11. The implantable medical device of claim 10, wherein thesecond high resistance section is formed by a second gap between thethird and fourth portions of the third layer, and wherein the at leastone tab of the first layer extending from the second surface ispositioned within the second gap.
 12. A method of making an implantablemedical device battery comprising: stacking a first electrode with asecond electrode, wherein the second electrode is separate from thefirst electrode, the second electrode including: a first layer formed ofa first material having a first continuous surface and a secondcontinuous surface opposite the first surface, wherein the firstmaterial is a conductive material; and a second layer positioned on thefirst surface of the first layer, the second layer formed of a secondmaterial different from the first material, wherein the second materialis lithium, wherein the second layer includes a first portion separatedfrom a second portion by a high resistance section, the high resistancesection having a greater resistance compared to the first and secondportions of the second layer to reduce a radial current loop size in thesecond electrode.
 13. The method of claim 12, wherein the conductivematerial is selected from one of stainless steel and nickel.
 14. Themethod of claim 12, further including forming the high resistancesection.
 15. The method of claim 14, wherein the high resistance sectionis a gap between the first and second portions of the second layer. 16.The method of claim 15, further including depositing an insulatingmaterial within the gap to maintain the gap between the first and secondportions of the second layer.
 17. The method of claim 15, wherein thefirst layer includes a tab extending from the first surface of the firstlayer, the method further includes: positioning the tab within the gapbetween the first and second portions of the second layer.
 18. Themethod of claim 17, further including coupling the tab to the firstlayer.
 19. The method of claim 18, wherein the tab is formed of a thirdmaterial that is different from the first material.